1. Field of the Invention
The present invention relates to an optical disc such as a DVD or the like. The present invention also relates to an information playback apparatus and information playback method for playing back information from such optical discs. Furthermore, the present invention relates to an information recording method for recording information on such optical discs.
2. Description of the Related Art
As described in Jpn. Pat. Appln. KOKAI Publication No. 2002-056543, optical discs with large recording capacities such as a DVD-RAM, DVD-R, DVD-RW, and the like have been developed and are in wide use. Such optical discs have a Part Version field indicating a version of a standard based on which that disc was prepared.
The Part Version field records a version number in the format of X.Y. A digit is assigned to each of X and Y. As a result, a version number such as 1.1, 2.1, 2.2, or the like is expressed.
At first, the Part Version field is set for the purpose of simply indicating the version of the standard. Hence, no rules are specified upon upgrading. For this reason, interpretation of the Part Version field by early disc drives is not coordinated. For example, early optical disc drives include models which do not check the version number in the Part Version field at all, and models which do not accept a disc if a number other than a specific version number is recorded in the Part Version field.
At present, upgrading rules are specified. The X value described in the Part Version field is changed if the latest version is incompatible with conventional discs. On the other hand, the Y value is changed if the latest version is compatible with conventional discs and a new specification is added. This additional specification is often incompatible with conventional discs.
Furthermore, in order to implement high-speed recording on DVD-RAM, DVD-R, and DVD-RW as recording media, specifications for high-speed recording are added. Such additional specifications for high-speed recording are compatible with the conventionally specified recording speeds. That is, an optical disc for which additional specifications for high-speed recording are specified is compatible with the conventional recording speeds and also new recording speeds.
Such an additional specification for high-speed recording is that which should change the Y value in terms of rules. However, it is troublesome to change Y by adding a new page to an existing standard every time a compatible recording speed is added. In consideration of this, an option BOOK is independently issued in association with recording speeds, and the version of this option BOOK is managed by a Revision number.
This is because optical disc drives which are already on the market often cannot handle new discs although they have compatibility, if Y is changed. Note that the Revision number adopts a format of A.B. However, this Revision number is not described on the disc.
Recently, discs which allow recording/playback at higher speed have been developed. As a result, it is difficult to manufacture discs which can achieve both recording at initially specified speeds and latest high-speed recording. In such case, an optical disc which is compatible with latest high-speed recording becomes incompatible with old discs. Hence, according to the conventional rules, the X value recorded on the Part Version field of an optical disc which is compatible with the latest high-speed recording is changed. However, since the X value is changed, a conventional optical disc drive which can perform only playback of an optical disc compatible with the latest high-speed recording can no longer perform playback in practice.
In practice, even when information is recorded at a conventional slowest speed by constraint on a disc compatible with the latest high-speed recording, data on the disc is never destroyed. Hence, the upgrading rule is changed, and the X value is changed if a change that does not allow playback is added.
Even when such rule change is to be made, some optical disc drives cannot perform any recording if the Y value is changed. In some cases, some optical disc drives cannot perform any playback if the Y value is changed. For this reason, the Y value cannot be changed if a specification that does not impair compatibility is made.
For this reason, the optical disc drive cannot detect any change in specification from the version information even when the specifications have changed. Also, as for the standard, if a specification is added without changing the version number, a change in standard can hardly be understood. Hence, a problem may be posed upon designing a drive that handles discs based on old specifications.